When causing a legged mobile robot, such as a bipedal mobile robot, to perform an operation of, for example, moving a certain object by pushing, the robot is subjected not only to a floor reaction force from a floor with which a distal portion of a leg thereof is in contact but also to a reaction force from the object. The reaction force received by the robot from an object as described above will be referred to as an object reaction force in the present description.
As a technology for generating a gait of a robot or carrying out motion control thereof in a state wherein an object reaction force is acting on a legged mobile robot as described above, there has been known a technology disclosed in, for example, Japanese Patent Laid-Open Publication No. H10-230485 by the inventor of the present application (hereinafter referred to as patent document 1). According to the technology, a desired gait is generated such that a dynamical balance condition in which a component (horizontal component), excluding a vertical component, of a moment produced about a desired ZMP (a desired floor reaction force central point) by a resultant force of an inertial force produced due to a motion of a robot and the gravity and an object reaction force acting on the robot is zero (a floor reaction force acting on the desired floor reaction force central point and the aforesaid resultant force are balanced out) is satisfied. Furthermore, according to the technology, even if an external force acting on the robot turns into an unexpected external force (even if a difference between a desired external force and an actual external force increases to a certain extent), a desired gait of the robot is adjusted such that a position of the center of gravity of the robot is balanced with a position of the center of gravity that makes it possible to maintain the dynamic balance of the robot.
In the meantime, when generating a gait of a robot to cause the robot to perform the operation of moving an object as described above, it is necessary to determine beforehand the trajectory (time series) of the desired values of acting forces applied from the robot to the object or the trajectory (time series) of the desired values of the aforesaid object reaction forces. An object reaction force is obtained by reversing the sign (direction) of an acting force applied from the robot to the object; hence, hereinafter, the trajectory of the desired values of the object reaction force will be representatively determined beforehand in the explanation herein.
In this case, the trajectory of the desired values of the object reaction force (hereinafter referred to as the desired object reaction force) is determined on the basis of, for example, a moving schedule for an object (a schedule of, for example, a timing and a method for moving an object).
However, an actual object reaction force acting on the robot does not necessarily always agree with a desired object reaction force. For instance, when starting from certain scheduled time an operation of moving an object by engaging a hand of the robot with the object, the desired object reaction force will suddenly change from zero to a certain value (≠0) at the scheduled time; however, there is a case where an actual object reaction force does not change at the scheduled time due to a shift in a positional relationship between the actual robot and the object. In such a case, a gait generated on the basis of a desired object reaction force trajectory is a gait that has been generated, expecting that the object reaction force changes at the aforesaid scheduled time; therefore, if an actual object reaction force does not change at the scheduled time, then the stability of the robot tends to be impaired. Further, there are many cases where even if an attempt is made to correct the posture of a robot on the basis of the difference between an actual object reaction force and a desired object reaction force, as in the aforesaid patent document 1, at the scheduled time, the posture of the robot cannot be immediately corrected to a stable posture.
The present invention has been made with a view of the above background, and it is an object thereof to provide a gait generating device of a legged mobile robot that is capable of generating a gait for causing a robot to perform an operation of moving an object, considering a case where a future acting force between the robot and the object deviates from a desired value, and of generating a gait of a robot such that the stability of a posture of the robot can be secured even if the acting force deviates from a desired value.